Studies on the induction of β-galactosidase in a cryptic strain of Escherichia coli

Abstract 1. 1. The absence of a galactosidase permease in a cryptic strain of E. coli was established. 2. 2. The kinetics and specificity of induction of β-galactosidase in this strain were studied and compared with a normal strain (with galactoside permease). 3. 3. The differential rate of synthesis of β-galactosidase in the cryptic is constant from the moment of inducer addition, at all levels of inducer which give measurable induction. This is in contrast to the situation in the normal strain where at sub-saturating concentrations of inducer, there is a lag and a period of increase in the differential rate of synthesis before a constant rate is attained. 4. 4. The increasing differential rate of synthesis in the normal was shown to be due to the action of the inducible galactoside permease. 5. 5. The constant differential rate in the cryptic and in the permease-blocked normal strain was discussed as evidence that the enzyme forming system for β-galactosidase does not increase in amount in response to inducer. 6. 6. Certain aryl-thiogalactosides are competitive inhibitors of induction in permeaseless strains. This result indicates that a sterically specific site, distinct from galactosidase or permease, is involved in induction.